#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
n = int(sys.stdin.readline().split(' ')[0])
f = []
for i in range(n-1):
    l = sys.stdin.readline().split(' ')
    f.append(int(l[0]))
on = []
off = []
for i in range(n-1):
    l = sys.stdin.readline().split(' ')
    off.append(int(l[0]))
    on.append(int(l[1]))

ans = 0
passgr = 0
for i in range(n-1):
    passgr += on[i] - off[i]
    ans += f[i] * passgr

print(ans)